The fixed-arch shield method of mining is particularly useful for the underground mining of bituminous sands, oil shales, and other friable mineral deposits. The technique is a refinement of the "Longwall" method of underground mining which is widely used in mining coal, phosphate, trona and other minerals.
The cutting machines used in all of these techniques are most often shearers, trepaners or ploughs, or combinations of these.
In the fixed-arch shield technique, as disclosed in the aforementioned co-pending application, a network of longitudinal operating tunnels are arranged and connected by transverse mining shields. The shields are formed from a plurality of adjacent half-arches which collectively form the shield. Rails are provided along the base of the shield and supported by the bases of the arches, and the mining equipment is moved along these rails. For a further description of this type of mining technique, reference is had to the aforementioned co-pending application.
The power supply used in this mining system is used in several ways. It is used to power the cutting drum in the case of shearers and trepaners, to plough the broken material into the face of the conveyor for removing the material from the mining area, to advance the plough if the plough is used as the primary excavator, and to advance the mining machinery along the working face. The present invention deals with the apparatus whereby the mining machinery is advanced along the shield as the mining process progresses.
Heretofore, the machinery was almost universally advanced by means of a chain and sprocket arrangement whereby the machine is equipped with drive sprockets which engage the links of a chain and pull the machinery ahead along the chain. With the chain being stretched the full length of the mining face and anchored at each end, the machinery may advance this entire length.
By its very nature, however, the prior art chain drive arrangement has certain limitations. Most significantly, the chain may stretch or may even break, thus requiring considerable down time for the apparatus. Of course the stretching of the chain also causes difficulties in that the chain must be constantly tightened or, unequal stretching of the links results in the chain not properly fitting the drive sprockets or causing excessive wear.
Periodically, efforts have been made to overcome the limitations of the chains drive by providing a more positive drive means along the mining face. Various forms of rack and pinion drive means have been somewhat successful in this regard. In such a construction, frequently the mined material conveyor is interconnected with the machinery in a manner to advance the mining machine.
By virtue of the development of the fixed-arch shield technique and the close integration of the mining machinery with the shield, the fixed arches are designed so that a continuous "rack" is provided by the shield along the full length of the mining face. Below the inner curved face of the fixed arch, there is a portion of the arch structure where the web of the arch along with the reinforcing side plates is exposed in a vertical section. With the arches lined up side-by-side to form the shield, these exposed portions of the web and the side plates collectively form a series of strong, evenly-spaced cleats in the nature of a "rack" upon which a suitable "pinion" drive can operate.
By this structure, considerably more power may be transmitted to the drive than could be absorbed by the conventional chain drive.
Accordingly, a primary object of this invention is to provide a drive mechanism for mining machinery used in the fixed-arch shield mining technique.
Still another object of this invention is a propulsion system for mining machinery which overcomes the disadvantages of prior art propulsion means.
A further object of this invention is to provide a drive mechanism for mining machinery for use in the fixed-arch shield technique wherein at least portions of the arches serve as the rack in a "rack and pinion" drive.
Still a further object of this invention is to provide a propulsion motor which is movable between a cutting position and a non-cutting position of the mining machinery.